\documentclass{standalone}
\usepackage{tikz}
\usepackage{ctex,siunitx}
\usepackage{tkz-euclide}
\usepackage{amsmath}
\usetikzlibrary{patterns, calc}
\usetikzlibrary {decorations.pathmorphing, decorations.pathreplacing, decorations.shapes,}
\begin{document}
\small
\begin{tikzpicture}[>=stealth,scale=0.65]
  \draw[<->] (0,6.5)node [right]{$p$}--(0,0)--(6,0) node [right]{{$t \; ^\circ \rm{C}$}};
  \draw(-6,0)--(0,0);
  \draw[color=black, ultra thick] (0,2.5)--(5,5);
  \draw [dashed] (0,2.5)--(-5,0);
  \node at (0,-.4){$O$}; \node at (-5,-.4){$-273$};
  \node at (-5,.4){$D$};
\end{tikzpicture}
\end{document}